Lavender is a herb, usually bearing purple flowers, that grows well in the UK. There are more than 20 varieties of lavender, including Spanish, French, woolly and yellow. A hardy plant, lavender can grow in most conditions, although it prefers full sun and slightly moist soil. A lavender plant that's over-watered will die. It is also susceptible to several diseases and pests.
Examine the stem of the lavender plant where it grows into the soil. If bark is sloughing off, the plant has received too much water and its roots have started to rot. Though the rest of the plant may look healthy, it will not live and needs to be removed. Dig around the base of the plant down to the bottom of the roots, using a trowel to pull it out of the ground. Discard in a garden waste bag or compost the remains of the lavender plant.
Check the flowers for signs of wilting. Wilted flowers mean the plant has not had enough water or that the plant has lavender shab disease. Examine the stems and bark of the plant closely, looking for small black dots. If the plant does not have any, it simply needs water. Black dots are mould that indicate shab disease. Put on your gardening gloves and remove the affected plant by the roots, using the trowel. Dispose of the plant by burning it or placing it in a garden waste bag.
Check the leaves of your lavender plant for signs of yellowing and curling. These are both signs of a disease called alfa mosaic virus, which is easily spread from one plant to another. If the leaves on your lavender plant show signs of this virus, put on your gardening gloves and dig around the base of the plant down to the roots. Pull the lavender plant out of the ground and immediately dispose of it in a garden waste bag or incinerator.